In the context of an airport navigation function (which makes it possible to display on a screen in the cockpit of an aircraft a map of the airport upon which is indicated, in particular, the current position of the aircraft), it is necessary to know the exact position of the aircraft when it is on the ground. The precision and the refresh rate of this position are determinant parameters for ensuring safety and the credibility of the displayed information, with respect to external references that can be seen by the pilot.
In order to determine its position in flight, the aircraft generally comprises positioning equipment which is associated with a satellite positioning system of the GPS or GALILEO or similar type, Such positioning equipment generally comprises an antenna which is mounted on the top of the aircraft, as well as a receiver which is linked with said antenna and which receives and processes the signals detected by the latter.
In the case of a GPS system, for example, the on-board positioning equipment which is intended for in-flight navigation generally delivers a position every second, which is not sufficient for creating an impression of movement of the aircraft on the display. Moreover, the current in-flight performance standards, with which this positioning equipment complies, do not cover the increased precision requirement on the ground (generally less than 10 meters), nor the phenomena associated with the environment encountered on the ground (presence of buildings and multiple reflections in particular).
This positioning equipment which is provided on the aircraft and which is perfectly suited to in-flight navigation is not therefore satisfactory for use in the context of airport navigation of the aforesaid type.
Another big disadvantage of a usual airport navigation function relates in particular to the display which is presented to the pilot. This display generally concerns an aircraft symbol which is presented at an estimated or measured position of the aircraft on an airport map, without however indication the orientation of said aircraft.